Prader- Willi syndrome is an uncommon multisystem genetic disorder caused by defects of chromosome 15 (15qll-ql3), often due to deletions or uniparental disomy The syndrome is characterized by neonatal hypotonia, dysmorphic facial features, short stature, motor and mental disabilities, behavioral changes, hyperphagia, precocious obesity and hypogonadotropic hypogonadism. We present a 17year-old woman, with a previous genetic diagnosis of Prader-Willi syndrome and BMI of 74 Kg/m2, that was admitted in anasarca, with marked cyanosis, dyspnea and oliguria. She presented high levels ofblood urea, creatinine and aminotransferases, in addition to hyperkalemia and hyperuricemia. She had been in regular use of fluoxetine during the last six months, and evolved with severe high bloodpressure and respiratory failure, which needed intensive care support. Moreover, sequéis and clear signs of recent selfinjuries were observed in her trunk, forearms and hands. The findings of morbid obesity, anasarca, self-injury, hyperuricemia and hypoxemia in Prader- Willi syndrome are emphasized.